In the coming year, investigation will focus on studies of the biophysical properties of the rabbit esophageal epithelium and how it is perturbed by H ion, and on the clinical value of electrical potential difference (PD) measurements in patients with reflux esophagitis and Barrett's epithelium. We will attempt to reproduce and characterize the damage of the rabbit esophagus created by in vivo acid perfusion by exposing the esophagus to H ion in vitro in the Ussing chamber. Na transport will be measured at various times during acid damage and those results correlated with light and electron microscopy and NaK ATPase measurements. In addition, the effect of H ion on the charge characteristics of the paracellular pathway will be defined with in vitro studies similar to those performed in other epithelia for this purpose. In humans with clinical history of reflux esophagitis but no gross mucosal lesion or in patients suspected of having Barrett's epithelium on either clinical, endoscopic or experimental grounds, we will correlate clinical course esophageal PD measurements, endoscopy, and light and electron microscopy. Such measurements will determine the sensitivity and usefulness of PD measurements as either a diagnostic or prognostic tool to study these diseases in man. In addition, human esophageal mucosal samples will be obtained at the time of esophageal surgery for cancer and will be mounted in the Ussing chamber for measurements of Na transport in this epithelium. Such studies will characterize the transport properties of the human epithelium and categorize them with other animal species that have been previously investigated.